<div class="field">
<%= f.label :staff_member_id %><br>
# Currently displays all staff members on every team, no matter what team is selected.
<%= f.collection_select :staff_member_id, StaffMember.all, :id, :first_name %>
</div>
...

#app/assets/javascripts/task_notes.js
$(document).ready(function(){

$("#team").on('change', function(){
alert("The new team id is: " + $(this).val() );
# The value (the id of the team) does update on selection option change.
# Now I need to specify that I want the select options for the staff members
# select box to update and show only staff members with this team_id
});